Data consumption via wireless devices has stimulated increasing demand for small, broadband, low-cost antennas that support multi-band operation. Space and weight constraints imposed by wireless devices, however, require few and/or small and often integrated antennas. While antennas including planar antenna structures such as patch antennas, for example, have a low profile, are light weight and incur low production cost, bandwidth capabilities of these antennas can be insufficient for use in multi-band wireless communication systems. Examples of wireless communication systems include Global System for Mobile Communications (GSM) 1800, Personal Communications Service (PCS) 1900, wideband code division multiple access standard IMT 2000, Bluetooth ISM (Industrial, Scientific, and Medical) and other wireless communication systems, for example.
A typical patch antenna 100 is shown in a side view in FIG. 1. The patch antenna 100 comprises a ground plane 102, a patch (also referred to as a conductor plate) 104, and a feed 106, for example a connection to a suitable coaxial cable. This type of antenna has an electrical length that typically corresponds with half the guide wavelength, λ0, wherein the guide wavelength corresponds with the wavelength of the electromagnetic field within the antenna at the resonant frequency, f0, at the transverse magnetic (TM) mode TM 01.
Various modifications to the type of antenna shown in FIG. 1, including openings in the patch 104 and/or the ground plane 102, have been made in the art to improve various aspects of antenna performance. Shorting structures including shorting posts and shorting walls for example, furthermore, have been used in combination with patch antennas to reduce the overall size of the patch antenna while attempting to maintain bandwidth. Resulting antennas have been reduced in electrical length to λ0/4 and below. Respective antennas have been employed in 3G IMT-2000 mobile handsets, for example. However, this type of antenna provides only marginally improved performance at the expense of significantly greater complexity, and can be difficult and expensive to manufacture.
It has been shown that the size of shorted-patch antennas, which are typically referred to as planar inverted-F antennas (PIFAs), can be further reduced to below λ0/4 in various ways, for example, by disposing shorting structures proximate a corner of a patch plate or by biasing, often referred to as loading, the PIFA. Further size reductions have been achieved by folding and or shaping the patch in certain ways to decrease the geometrical size of the antenna while maintaining the guide wavelength. FIG. 2 illustrates a folded shorted-patch antenna 200 that has been reduced in length to about λ0/8. This structure is based on a shorted ¼ wave patch that has been folded over itself and laid on a ground plane. This results in a structure that is only about λ0/8 long as shown. The folded shorted-patch antenna includes two patches, a first patch 204 that is shorted to the ground plane 202 with a metal wall 207. This patch can be folded from the surface skin of the ground plane 202. A second patch 208 is shorted to the ground plane 202 with a metal wall 205 and is provided with a feed point 206. Patch 205 can be formed from an initial patch which can be folded over itself thereby becoming a patch half the size of the original. The wall 207 is spaced to form a gap between itself and the patch 208. Moreover, printed antennas with a surface area of only about 25% of that of a patch antenna 100 as shown in FIG. 1 have been made possible by incorporating adequately disposed slots and shorting pins. U.S. Pat. Nos. 4,980,694, 5,355,143 and 6,914,563, and United States Patent Application Publication Nos. 2002/0175871, 2003/0107518 and 2008/0129625 describe examples of the noted known solutions.
While patch antennas with notably reduced sizes have been achieved, bandwidth characteristics have been somewhat neglected. Therefore there is a need for a solution that overcomes at least one of the deficiencies in the art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present technology. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present technology.